RUI: Exploring the Origin of the Rarest Stable Isotopes via Photon-Induced Activation Studies at the Madison Accelerator Laboratory

恒星的核反应和恒星爆炸是如何从大爆炸遗留下来的氢和氦中锻造出元素的，这是核天体物理学中一个长期但及时的研究课题。人们对恒星中通过核聚变反应产生铁以下元素已经有了相当全面的了解，但是关于铁以外元素产生的重要细节仍然令人费解。拟议的研究旨在推进核天体物理学前沿课题的基础知识——铁以外元素和地球上自然存在的最稀有稳定同位素的合成。导致这种合成的天体物理现象被称为p过程。虽然在计算机上模拟p过程核合成是一项艰巨的任务，但通过执行关键测量可以取得重大进展，这些测量限制了用于计算未知恒星反应速率的模型。此外，拟议的研究将在新开设的麦迪逊加速器实验室（MAL）的加速器环境中为本科生创造丰富的研究体验。MAL是詹姆斯麦迪逊大学校园内独特的轫致辐射设施。学生们将有一个极好的机会在一个基于加速器的环境中亲身参与，他们将能够参与核天体物理学的前沿研究。这一经历是他们作为未来研究人员培训的重要组成部分，将为他们提供在工业、国家实验室和大学从事STEM职业所需的技能。本课题的研究重点是通过实验确定八种光中子反应的基态反应速率，这八种光中子反应分别是：64Zn(gamma,n)63Zn, 70Ge(gamma,n) 69Ge,74Se(gamma,n)73Se, 78,80Kr(gamma,n)77,79Kr, 84,86Sr(gamma,n)83,85Sr和90Zr(gamma,n) 89Zr。我们感兴趣的8个富含质子的稳定原子核属于a124区域，这个区域在目前的恒星演化模型中是出了名的生产不足。在实验室中，人们只能接触基态的目标原子核，因此在p过程的高温状态下，由激发态贡献主导的恒星光分解反应速率不能直接在实验中受到约束。通过MAL的实验，我们可以提供核科学输入（通过反反应运动学）来约束核反应模型的关键参数，即与光中子反应特别相关的伽马射线强度函数。考虑到即使是一个p核的产生也涉及大量的核反应，任何与p过程路径相关的光分解反应的新测量都将为核合成计算奠定更坚实的基础。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The question of how nuclear reactions in stars and stellar explosions have forged the elements out of hydrogen and helium leftover from the Big Bang is a longstanding but timely research topic in nuclear astrophysics. There is a fairly complete understanding of the production of the elements up to iron by nuclear fusion reactions in stars but important details concerning the production of the elements beyond iron remain puzzling. The proposed research aims to advance fundamental knowledge on a forefront topic in nuclear astrophysics - the synthesis of elements beyond Fe and of the rarest stable isotopes naturally occurring on Earth. The astrophysical phenomenon responsible for this synthesis is termed the p-process. Though simulating the p-process nucleosynthesis on a computer is a daunting task, significant progress can be made by performing key measurements which constrain the models that are used to calculate the unknown stellar reaction rates. Moreover, the proposed research will create an rich research experience for undergraduates in an accelerator-based environment at the newly opened Madison Accelerator Laboratory (MAL). MAL is a unique bremsstrahlung facility on the campus of James Madison University. The students will have an excellent opportunity for hands-on participation in an accelerator-based environment and they will be able to participate in cutting-edge research in nuclear astrophysics. This experience is an important part of their training as future researchers and will provide them with skills necessary to pursue STEM careers in Industry, at National Laboratories and Universities.The focus of this proposal's research program is to determine experimentally the ground state reaction rates for eight photo-neutron reactions which are to be investigated by photon-induced activation at MAL. The eight photo-neutron reactions are: 64Zn(gamma,n)63Zn, 70Ge(gamm,n)69Ge,74Se(gamma,n)73Se, 78,80Kr(gamma,n)77,79Kr, 84,86Sr(gamma,n)83,85Sr and 90Zr(gaamma,n)89Zr. The eight proton-rich stable nuclei of interest belong to the region A 124 which is notoriously under produced by the current stellar evolution models. In the laboratory one only has access to target nuclei in the ground state and so the stellar photodisintegration reaction rates, dominated by excited state contributions at the high temperature regime of the p-process, cannot be directly constrained experimentally. With the experiments at MAL, we can instead provide nuclear science input (through inverse reaction kinematics) to constrain crucial parameters of the nuclear reaction models, i.e. gamma ray strength function especially relevant for photo-neutron reactions. Considering the very large number of nuclear reactions involved in the production of even a single p-nucleus, any new measurement of photodisintegration reactions relevant to the p-process path will put the nucleosynthesis calculations on a firmer foundation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.